We propose to study the electrophysiology of an ischemic area, taking advantage of a new technique for directly visualizing areas of anoxia, NADH fluorescence photography. NADH fluorescence arises from anoxic mitochondria and correlates well with biochemical evidence of tissue anoxia. Recently it has been applied to define areas of myocardial anoxia using a xenon flash photographic technique. The advantages of the technique are that it is noninvasive and nondestructive, and it offers excellent temporal and spatial resolution of anoxic areas. Using NADH fluorescence photography to define the ischemic areas, we will study in the isolated rabbit heart the electrophysiology of experimentally induced ischemic areas. Particular attention will be placed on the relationship between electrophysiologic abnormalities versus electrode location within or near the ischemic area. Electrophysiologic parameters measured will include ST segment epicardial mapping, tissue resistivity, extracellular and intracellular electrograms, and determinations of refractoriness. The effects of antiarrhythmic drugs on tissue on either side of the ischemic border will be evaluated. In all studies the ability of NADH fluorescence photography to precisely locate the ischemic area will be exploited. This work will describe the electrophysiologic abnormalities across a well defined ischemic border, and advance the understanding of the electrophysiology of ischemic areas.